Farkon Armature a cikin Alternators
Takardar da Armature Reaction
Armature reaction a cikin alternator yana shi ne mafi inganci na sauki na armature zuwa sauki na main magnetic field na alternator ko synchronous generator.
Interaction na Magnetic Field
Idan armature ta da current, sauki na ta ya kula da main field, wanda yake iya haɗa da distortion (cross-magnetizing) ko reduction (demagnetizing) na main field flux.
Power Factor Influence
A unity power factor, angle between armature current I and induced emf E, ita ce zero. Yana nufin, armature current and induced emf suna cikin phase daban-daban. Amma ana sani a cikin littattafai cewa emf induced a cikin armature yana kasance saboda changing main field flux, linked with the armature conductor.
Idan field ta excited by DC, main field flux ita ce constant in respect to field magnets, amma ita ce alternating in respect of armature saboda akwai relative motion between field and armature a cikin alternator. Idan main field flux na alternator in respect of armature zai iya canzawa a haka
Then induced emf E across the armature is proportional to, dφf/dt.
Hence, from these above equations (1) and (2) it is clear that the angle between, φf and induced emf E will be 90o.
Now, armature flux φa is proportional to armature current I. Hence, armature flux φa is in phase with armature current I.
Again at unity electrical power factor I and E are in same phase. So, at unity power factor, φa is phase with E. So at this condition, armature flux is in phase with induced emf E and field flux is in quadrature with E. Hence, armature flux φa is in quadrature with main field flux φf.
As this two fluxes are perpendicular to each other, the armature reaction of the alternator at unity power factor is purely distorting or cross-magnetising type.
As the armature flux pushes the main field flux perpendicularly, distribution of main field flux under a pole face does not remain uniformly distributed. The flux density under the trailing pole tips increases somewhat while under the leading pole tips it decreases.
Lagging and Leading Loads
At leading power factor condition, armature current “I” leads induced emf E by an angle 90o. Again, we have shown just, field flux φf leads, induced emf E by 90o.
Again, armature flux φa is proportional to armature current I. Hence, φa is in phase with I. Hence, armature flux φa also leads E, by 90o as I leads E by 90o.
As in this case both armature flux and field flux lead, induced emf E by 90o, it can be said, field flux and armature flux are in the same direction. Hence, the resultant flux is simply arithmetic sum of field flux and armature flux. Hence, at last, it can be said that armature reaction of alternator due to a purely leading electrical power factor is the magnetizing type.
Unity Power Factor Effect
Armature reaction flux ita ce constant in magnitude and rotates at synchronous speed.
Armature reaction ita ce cross magnetising when the generator supplies a load at unity power factor.
When the generator supplies a load at leading power factor the armature reaction is partly demagnetising and partly cross-magnetising.
When the generator supplies a load at leading power factor the armature reaction is partly magnetising and partly cross-magnetising.
Armature flux acts independently of main field flux.
